Grappling dummies - Your experience/advice?

So I'm having trouble making it to various classes as a result of school, and I was wondering about grappling dummies. Would anyone recommend them for the busy, dorm-bound student? I figure I could use one just for the sake of retaining/improving my muscle memory so I don't get "ring rust".

I have a cheap Amber dummy I picked up on eBay. It was really helpful while I was healing up from an injury. I think it'd be useful for what you're describing when you can't make it to class often (say, less than 3 times/week).